Various dispensers of this kind have been described in the literature. For example, the U.S. Pat. No. 4,256,242 (Christine) discloses a liquid soap dispenser comprising a housing, a collapsible bag for holding the liquid soap product and an operating lever or handle for actuating controlled amounts of soap from the bag. The collapsible bag is connected to an outlet by means of a flexible conduit which comprises a pump.
These known type of dispensers offer hygiene and ease of handling for the user. However, one problem with this kind of dispensers resides in the fact that only a small amount of liquid soap may be dispensed at a time, due to the limited capacity of the pump. The amount is usually not more than 0.5 to 1 ml.
Another problem which is commonly encountered is the fact that the dispenser may run out of soap unnoticed, which causes annoyance and hygiene risks for the user. Frequently checking by janitors will reduce the likelihood of a soap dispenser being out of soap for a long time, but this is not an economical solution.
It has also been suggested in the European patent application 110,686 (Kimberley-Clark) to provide the soap dispenser with a window through which the reservoir level may be seen. This offers only a partial solution to the above mentioned problems, because it is not possible to determine when exactly the reservoir will run out of soap. It may even lead to a waste of liquid soap product if it becomes customary to replace the reservoirs before they are completely emptied.